Technical Field
The present disclosure relates to a hydraulic power transmission device and in particular to a hydraulic power transmission device for transmitting power from an engine to a transmission via a fluid.
Background Art
A torque converter that is provided with a lock-up device is known as an example of a hydraulic power transmission device. A lock-up device is a mechanism for mechanically coupling a front cover and a turbine, and is arranged in the space between the turbine and the front cover.
A lock-up device has a clutch portion and a damper mechanism. The clutch portion has a piston that has a friction member, for example. In this device, when the piston moves and the friction member is pressed against the front cover, power is transmitted from the front cover to the damper mechanism via the piston. The damper mechanism has a plurality of elastic members and an output-side member to which power is transmitted via the elastic members. The output-side member is fixed to the turbine.
Such a lock-up device has conventionally been provided with a dynamic damper. Providing a dynamic damper makes it possible to reduce a torque fluctuation peak that appears in the vicinity of the resonance frequency of the damper mechanism.
One large torque fluctuation peak can be suppressed by providing the dynamic damper as described above, but on the other hand, a torque fluctuation peak also appears at two locations, namely a rotational speed higher than and a rotational speed lower than the rotational speed at which the one large peak appears. Out of these two peaks, the peak on the lower rotational speed side appears in a rotational speed range that is lower than the normal rotational speed, and therefore is not a problem during use. However, the peak on the higher rotational speed side commonly appears in the normal rotational speed range, thus making it necessary to attenuate this peak on the higher rotational speed side, and a device for achieving this is shown in Japanese Patent Application Publication No. 2011-58557A.